1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for reporting a channel quality indicator in a wireless communication system.
2. Related Art
The next-generation multimedia wireless communication systems which are recently being actively researched are required to process and transmit various pieces of information, such as video and wireless data as well as the initial voice-centered services. The 4th generation wireless communication systems which are now being developed subsequently to the 3rd generation wireless communication systems are aiming at supporting high-speed data service of downlink 1 Gbps (Gigabits per second) and uplink 500 Mbps (Megabits per second). The object of the wireless communication system is to establish reliable communications between a number of users irrespective of their positions and mobility. However, a wireless channel has abnormal characteristics, such as path loss, noise, a fading phenomenon due to multi-path, inter-symbol interference (ISI), and the Doppler Effect resulting from the mobility of a user equipment. A variety of techniques are being developed in order to overcome the abnormal characteristics of the wireless channel and to increase the reliability of wireless communication.
Meanwhile, with the employment of machine-to-machine (M2M) communication and with the introduction and distribution of various devices such as a smart phone, a table personal computer (PC), etc., a data requirement size for a cellular network is increased rapidly. To satisfy a high data requirement size, various techniques are under development. A carrier aggregation (CA) technique, a cognitive radio (CR) technique, or the like for effectively using more frequency bands are under research. In addition, a multiple antenna technique, a multiple base station cooperation technique, or the like for increasing data capacity within a limited frequency are under research. That is, eventually, the wireless communication system will be evolved in a direction of increasing density of nodes capable of accessing to an area around a user. A wireless communication system having nodes with higher density can provide a higher performance through cooperation between the nodes. That is, a wireless communication system in which each node cooperates has a much higher performance than a wireless communication system in which each node operates as an independent base station (BS), advanced BS (ABS), node-B (NB), eNode-B (eNB), access point (AP), etc.
Meanwhile, an inter-cell interference (ICI) problem may occur between respective nodes in a multi-node system. The ICI may have an influence on a femto user equipment (UE) or pico UE served by a femto cell or pico cell having a smaller service coverage from a macro cell in general. 3GPP solves the ICI problem through an enhanced inter-cell interference coordination (eICIC) session.
UE may report a channel quality indicator (CQI) to a BS. The BS may use the CQI received from the UE when scheduling. However, if the CQI is reported by the conventional method in a situation where various techniques are applied to solve the ICI problem, a channel environment improvement gain obtained by solving the ICI problem cannot be directly applied onto a system.
There is a need for an effective CQI reporting method to solve the ICI problem in the multi-node system.